Method of melting and alloying metals



Nov. 14, 1961 R. A. PERKINS 3,008,821

METHOD OF MELTING AND ALLOYING METALS Filed June 17, 1959 2 sheets-sheet 1 Solid l I I I I I I I I I I TEMPERATURE I (1 1 C3 C2 C4 TUNGSTEN CONTENT Nov. 14, 1961 R. A. PERKINS METHOD OF MELTING AND ALLOYING METALS 2 Sheets-Sheet 2 Filed June 17, 1959 50% laaoc.

Beta Tungsten I Llquld I L|qu|d+Tungsfen m m l 0 235%? 3-0 40 TUNGSTEN W0 u 0 m O m P w m o A555 5.5022.

3 I mm TE NP E m W R E m R 8 S E T U W M 6 E W T m 4 M L Hm O T 2 WWW ATTORNEY United States Patent 3 008 821 METHOD or MELTING AND ALLOYING METALS Roger A. Perkins, Fair Oaks, Calif., assignor to Union Carbide Corporation, a corporation of New York Filed June 17, 1959, Ser. No. 821,031 12 Claims. (Cl. 75135) This invention relates to a method for alloying, melting, and casting metals and alloys and, more particularly, to a method of producing simple or complex, high-purity homogeneous tungsten-containing alloys of such reactive refractory metals as zirconium, hafnium, vanadium, chromium, columbium, and alloys thereof.

As is well-known, the addition of other elements to a metal or alloy will, in many instances, improve the properties of that metal or alloy. '-For example, the element tungsten may raise the melting point, impart greater strength at room temperature, and/ or enhance corrosion resistance of metals or alloys. However, due to the high melting point and high density of tungsten and the aflinity for carbon, oxygen and nitrogen which tungsten and the reactive refractory metals exhibit, the alloying of tungsten with-other metals and alloys, and particularly with reactive refractory metals and alloys, is very dif ficult.

One of the most commonly used processes for melting reactive refractory metals is are melting under an inert atmosphere or a vacuum in a water-cooled metal crucible. This process is commonly known as cold-mold arc melting. In this process, only a small portion of the charge is molten at one time since liquefaction and solidification is a continuous and integral part of the process, thereby rendering difficult the production of high-quality ingots with homogeneous chemical composition. For example, attempts to produce chemically homogeneous titaniumtungsten alloys by this process have shown that a rigorous and complex melting schedule must be followed. For example, to obtain a chemically homogeneous titaniumtungsten ingot by this process, the ingot must be remelted several times.

In the cold-mold arc melting process either a consumable or nonconsumable electrode can be employed. If a consumable electrode is used, during melting operations, the melt spatters and adheres to the walls of the cold mold. The adherence of the metal spatter to the walls of the mold results in the production of ingots that have poor surface quality. This necessitates subsequent machining of the ingot so that it is in a condition suitable for fabrication.

In addition, cold-mold arc melting is a dynamic process which is diflicult to control and which does not readily bind itself to pouring of melts for the production of castings except by employing high-power inputs and split-second timing. However, even by employing such controls, casting temperature is diflicult to control, holding time for refining and adjusting composition is not available, and the entire melt must be poured in one tap. Also, from a safety point of view this is not a desirable op eration.

Another approach to the problem of melting, casting, and alloying metals, and particularly reactive refractory metals, is to use a skull melting technique, wherein the water-cooled metal crucible is replaced by a solid crucible or a skull of the metal or alloy being melted, and reinforced by an insulating refractory such as graphite. Heat for melting is supplied by electric are from consumable or nonconsumable electrodes. In this process, a charge of metal or alloy is progressively arc melted until a relatively large pool of the metal or alloy is obtained. Heat flow from the pool through the reinforcing insulating refractory is controlled so that a layer of solidified metal or skull is produced, generally one inch in thickness or greater. The heat flow is controlled by cooling the skull and by regulating the rate of heat input. This technique has met with some-degree of success. However, due to the necessity of maintaining a critical thermal balance during melting, this process is inherently expensive and one which requires exceptional skill to result in the production of good-quality, reactive metal alloy castings.

Accordingly, it is an object of this invention to provide a process for producing high-purity, homogeneous tungsten-containing alloys.

Another object of this invention is to provide a process for the production of high-purity, homogeneous tungstencontaining alloys, wherein the entire melt can be held in a molten state to controlled temperature, to adjust the composition or to refine the melt.

A further object of this invention is to provide a process for the production of high-purity, homogeneous tungstencontaining alloys, wherein the Weight and composition of the material cast can be closely controlled and regulated.

A still further object of this invention is to provide a process for the production of high-purity, homogeneous tungsten-containing alloys, wherein a portion of the total melt can be cast and the remainder held in a liquid state, thus enabling the casting of the alloy in desired size and shape.

Other aims and advantages of this invention will be apparent from the following description and appended claims.

According to the present invention the novel process for producing high-purity, homogeneous tungsten-containing alloys comprises heating to a molten state at least one metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, chromium, columbium, and alloys thereof and from 0 parts by weight tungsten to substantially all of a predetermined amount of tungsten in the final alloy in a tungsten crucible in a nonreactive atmosphere, and maintaining the temperature of the molten metal at the temperature at which a molten metal having a composition corresponding to that in the finally alloy approaches equilibrium with the tungsten crucible, thereby forming a tungsten-rich composition at the melt-crucible interface which inhibits further dissolution of the tungsten crucible; subsequently removing the molten metal from the tungsten crucible to produce the tungsten-containing alloy.

In the drawings:

FIGURE 1 is a hypothetical equilibrium diagram for a binary tungsten-containing alloy.

FIGURE 2 is a graphic representation of melting data with phase boundaries for the titanium-tungsten system.

FIGURE 3 is a graph illustrating the effect of holding time on tungsten pick-up in the melting of titaniumtungsten alloys.

The process of this invention is applicable to the production of tungsten-containing alloys of metals and other alloys whose melting point is raised by the addition of tungsten. Included among these are the tungstencontaining alloys of reactive refractory metals, such as titanium, zirconium, hafnium, vanadium, chromium, columbium, and alloys thereof, in either binary, ternary, or more complex alloy systems.

The heat for melting the metal or alloy in the tungsten crucible can be supplied by resistance, induction, or are heating. Induction heating is preferred, however, because with such heating, melting is rapid, heating is uniform, and the magnetic field causes stirring of the melt. If other than induction heating is used, it may be desirable to employ suitable means to obtain a stirring of the melt.

Regardless of the type of heating employed, it is necessary that melting operations be carried out in a nonreactive atmosphere, e.g., under vacuum or the protection of an inert atmosphere, such as in argon or helium gas, to protect the crucible from contamination while it is hot.

The tungsten crucible, consisting of tungsten with incidental impurities, can be formed in a variety of ways, e. g., slip-casting, pressing and sintering, or fabricating from sheet metal. The tungsten crucible of this invention can be used as liners in refractory crucibles or as separate crucibles. When they are employed as separate crucibles, they are preferably insulated with a suitable refractory material such as zirconi'a, to prevent heat loss. In addition, the crucible can be mounted in a suitable tilting mechanism to permit easy pouring of the heat into ingot molds or castings.

In practicing the process of this invention, the metal or alloy in the tungsten crucible is heated until molten at which time the molten material commences to dissolve the tungsten crucible. As the temperature of the molten material is increased, the composition of the molten material is altered by the addition of a predetermined amount of tungsten. This tungsten addition can comprise from part by weight tungsten to substantially all of a predetermined am-ount of tungsten in the final alloy from a source other than the tungsten crucible, either in elemental or alloy form, or the tungsten addition can be from the tungsten crucible by the dissolving of the tungsten crucible by the molten material, or a portion of the tungsten can be added, either in elemental or alloy form, from a source other than the tungsten crucible and the remainder added from the tungsten crucible. The temperature of a molten material having a composition corresponding to that in the final alloy is determined from the appropriate equilibrium diagram and the molten material in the tungsten crucible is heated to this temperature and held constant while the molten material approaches equilibrium with the tungsten crucible. As equilibrium is approached between the molten material and the tungsten crucible, a tungsten-rich solid or semi-solid composition forms initially at the melt-crucible interface. The formation of this tungsten-rich composition at the melt-crucible interface, as equilibrium is approached, inhibits further dissolution of the tungsten crucible by the molten material. The tungsten content of the molten material is defined by the highest temperature at which equilibrium is approached between the molten material and the tungsten crucible. However, to a minor extent, alloy composition is dependent upon the holding time, i.e., the rate at which equilibrium is approached and the rate at which tungsten dilfuses throughout the molten material, thereby insuring homogeneity of the alloy produced.

In addition, since the composition of the tungsten-containing alloy is defined by the highest temperature at which equilibrium between the molten material and the tungsten crucible is approached, once equilibrium is approached, the molten material may be held at that temperature or at a lower temperature without altering the tungsten content of the alloy.

Referring specifically, by way of example to FIGURE 1, it may be seen that, in a simple binary system at temperature T liquid of composition C is in equilibrium with solid composition C The solid composition C in this invention is formed initially at the melt-crucible interrfiace. .As the temperature is increased to T the liquid of composition C is in equilibrium with solid composition C From this it may be seen that melt composition is defined and controlled by the temperature of the melt.

To illustrate the process of this invention, titaniumtungsten alloys containing 4 to 30 weight percent tungsten and the balance titanium with incidental impurities were prepared by melting (induction heating in an argon atmosphere) commercially pure titanium scrap in a tungsten crucible. The crucibles were mark by a slip-casting process and measured four inches inside diameter, eight inches high, and a one quarter inch wall thickness. The crucibles were insulated with granulated zirconia refractory and mounted in a tilting mechanism to permit pouring of the melts. The temperature was controlled by regulating power input and was measured by means of an optical pyrometer. The results are set forth below:

Melt Melt Tungsten Titanium Charged, Weight Lb. Temp Time, Content,

0. Min. Weight Percent In FIGURE 2, which shows phase boundaries for the titanium-tungsten system, a portion of the melting data obtained in these melts were set forth. 'From these results, it may be seen that the tungsten content of the alloy is defined by the temperature of melting.

In FIGURE 3, which shows the effect of the holding time on tungsten pick-up, a portion of the melting data obtained in these melts were set forth. From these results, it may be seen that equilibrium with tungsten crucible is approached rapidly and the melt ceases to dissolve the crucible in about three minutes holding time. The holding of the melt at these temperatures for longer periods of time results in no substantial tungsten pick-up by the melt. In addition, it may be seen that melt size has little, if any, effect on the alloy composition.

All of the above melts were fluid and poured clean. The resulting ingots were of good quality and soundness. Typical impurity contents were about 0.11 percent oxygen and 0.0058 percent hydrogen. All ingots had a homogeneous chemical composition.

To further illustrate this invention alloys containing between about 5 and 18 weight percent tungsten were prepared by adding tungsten as part of the charge and melting (induction heating in an argon atmosphere) at a temperature calculated to give the charged composition. An

ingot cast from those melts previously set forth containing 14.72 weight percent tungsten was remelted in a tungsten crucible. Thercsult is set forth below:

Melt Melt Tungsten Charge Weight, Lb. Temp, Time, Content,

0. Min. Weight Percent lowed is that heretofore set forth. The results are as set forth below:

Charge Melt Melt Tungsten Material Charged Weight, Temp, Time, Content,

Lb. 0. Min. Weight Percent 6% Al, 4% V, bal. Ti alloy--. 3.87 1, 730 4. 75 5.30 2.5% Sn, 5% Al, bal. Ti alloy 2.19 1, 730 37 75 6. 24 Zirconium Sponge 4. ()0 4. 00 6. 80 Electrolytic Chromium 3.00 1, 850 4. 00 10.?0

From the data set forth to illustrate this invention, it may be seen that a unique expedient, low-cost process for melting, alloying, and casting metals and alloys with tungsten is provided that results in the production of highquality, homogeneous tungsten-containing alloys.

What is claimed is:

1. A process for preparing high-purity, homogeneous, tungsten-containing alloys comprising heating to a molten state in a tungsten crucible in a non-reactive atmosphere at least one member selected from the group consisting of the metals titanium, zirconium, hafnium, vanadium, chromium and columbium; maintaining the temperature of the molten metal at the temperature at which a molten metal having a composition corresponding to that in the final alloy approaches equilibrium with said tungsten crucible, thereby forming a tungsten-rich composition at the melt-crucible interface which inhibits further dissolution of said tungsten crucible; and removing said molten met-a1 from said tungsten crucible to produce said tungsten-containing alloy.

2. The process in accordance with claim 1, wherein the selected metal is titanium.

3. The process in accordance with claim 1, wherein the selected metal is zirconium.

4. The process in accordance with claim 1, wherein the selected metal is chromium.

S. A process for preparing high-purity, homogeneous, tungsten-containing alloys comprising heating to a molten state in a non-reactive atmosphere in a tungsten crucible a predetermined amount of tungsten and at least one member selected from the group consisting of the metals titanium, zirconium, hafnium, vanadium, chromium and columbium; maintaining the temperature of the molten metals at a temperature at which a molten metal having a composition corresponding to that in the final alloy approaches equilibrium with said tungsten crucible, thereby forming a tungsten-rich composition at the melt-crucible interface which inhibits further dissolution of said tungsten crucible; and removing said molten metal from said crucible to produce said tungsten-containing alloy.

6. The process in accordance with claim 5, wherein the selected metal is titanium.

7. The process. in accordance with claim 5, wherein the selected metal is Zirconium.

8. The process in accordance with claim 5, wherein the selected metal is chromium.

9. A process for the production of high-purity, homogeneous, tungsten-containing alloys comprising melting in a tungsten crucible in a non-reactive atmosphere at least one member selected from the group consisting of the metals titanium, zirconium, hafnium, vanadium, chromium and columbium; increasing the temperature of the molten metal to increase the tungsten content of said molten metal to that temperature at which a molten metal having a composition corresponding to that in the final alloy approaches equilibrium with said tungsten crucible, thereby forming a tungsten-rich composition at the meltcrucible interface which inhibit further dissolution of said tungsten crucible; and removing said molten metal from said tungstein crucible to produce said tungsten-containing alloy.

10. The process in accordance with claim 9, wherein the selected metal is titanium.

11. The process in accordance with claim 9, wherein the selected metal is zirconium,

12. The process in accordance with claim 9, wherein the selected metal is chromium.

References Cited in the file of this patent UNITED STATES PATENTS 2,895,849 Perlman July 21, 1959 

1. A PROCESS FOR PREPARING HIGH-PURITY, HOMOGENEOUS, TUNGSTEN-CONTAINING ALLOYS COMPRISING HEATING TO A MOLTEN STATE IN A TUNGSTEN CRUIBLE IN A NON-REACTIVE STMOSPHERE AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF THE METALS TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM, CHROMIUM AND COLUMBIUM, MAINTAINING THE TEMPERATURE OF THE MOLTEN METAL AT THE TEMPERATURE AT WHICH A MOLTEN METAL HAVING A COMPOSITION CORRESPONDING TO THAT IN THE FINAL ALLOY APPROACHES EQUILIBRIUM WITH SAID TUNGSTEN CRUCIBLE, THEREBY FORMING A TUNGSTEN-RICH COMPOSITION AT THE MELT-CRUCIBLE INTERFACE WHICH INHIBITS FURTHER DISSOLUTION OF SAID TUNGSTEN CRUCIBLE, AND REMOVING SAID MOLTEN METAL FROM SAID TUNGSTEN CRUCIBLE TO PRODUCE SAID TUNGSTEN-CONTAINING ALLOY. 